rendezvous with a comet
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Rendezvous with a CometRendezvous with a Comet
Courtesy: Pat Rawlings - Deep Impact -NASA & JPL
IntroductionIntroduction
The history of comet watching dates back to 1000 BC from the Chinese records and Chaldea, a place in present Iraq.
Comets have been regarded as omen, even as recently as 1986. Battle of Hastings - 1066
Today Astronomer study Comets from scientific perspectives, and our understanding of these fascinating objects have grown tremendously.
The history of comet watching dates back to 1000 BC from the Chinese records and Chaldea, a place in present Iraq.
Comets have been regarded as omen, even as recently as 1986. Battle of Hastings - 1066
Today Astronomer study Comets from scientific perspectives, and our understanding of these fascinating objects have grown tremendously.
Dirty SnowballsDirty Snowballs
Comets are dusty chunk of ice During each orbit around the sun they
partially vaporize Have elliptical Orbits
Comets are dusty chunk of ice During each orbit around the sun they
partially vaporize Have elliptical Orbits
Courtesy: Calvin J. Hamilton
Structure of a CometStructure of a Comet
Solar heat vaporizes the nucleus to produce Coma - Hydrogen gas
Envelope Dust tail Ion tail
Solar heat vaporizes the nucleus to produce Coma - Hydrogen gas
Envelope Dust tail Ion tail
Courtesy: Deep Impact - NASA & JPL
Orbits of CometsOrbits of Comets
Elliptical in Shape Randomly oriented
Elliptical in Shape Randomly oriented
Sun
Comet
Earth
Perihelion distance
Aphelion distance
Comet HuntersComet Hunters
Comet are named by International Astronomical Union (IAU) after the person who first discovers them.
Many comets are discovered by amateur astronomers.
Charles Messier, E. E. Bernard, Shoemaker and Levy, Hale and Bopp, Ikeya, Seki and Hayakutake are popular comet hunters.
Comet are named by International Astronomical Union (IAU) after the person who first discovers them.
Many comets are discovered by amateur astronomers.
Charles Messier, E. E. Bernard, Shoemaker and Levy, Hale and Bopp, Ikeya, Seki and Hayakutake are popular comet hunters.
Origins of CometsOrigins of Comets
Comets are thought to be the left over debris from during the time of formation of the solar system.
The elliptical orbits of comets suggest that they underwent gravitational pull from the giant planets.
This all lead us to infer two possible locations where comets could start their journey towards the sun.
Comets are thought to be the left over debris from during the time of formation of the solar system.
The elliptical orbits of comets suggest that they underwent gravitational pull from the giant planets.
This all lead us to infer two possible locations where comets could start their journey towards the sun.
Possible Homes for CometsPossible Homes for Comets
Kuiper Belt Oort Cloud
Kuiper Belt Oort Cloud
Courtesy - Deep Impact - NASA - JPL
Kuiper BeltKuiper Belt
Discovered by Gerard Kuiper in 1951 The belt is 30 to 500 AU from the Sun The plane of the belt is close the to the
ecliptic Probably contains more than 100,000
objects Some of these objects are 100 km or larger
in diameter
Discovered by Gerard Kuiper in 1951 The belt is 30 to 500 AU from the Sun The plane of the belt is close the to the
ecliptic Probably contains more than 100,000
objects Some of these objects are 100 km or larger
in diameter
Oort CloudOort Cloud
Hypothesized by a Dutch Astronomer Jan Oort in 1950.
Shape is spherical distribution around the Sun.
50,000 AU from the Sun. May contain 5 trillion objects. Probably created 4.6 billion years ago.
Hypothesized by a Dutch Astronomer Jan Oort in 1950.
Shape is spherical distribution around the Sun.
50,000 AU from the Sun. May contain 5 trillion objects. Probably created 4.6 billion years ago.
Comets and their periodsComets and their periods
Jupiter-family: Kuiper belt 20 years. Gravitational perturbations by Neptune Elliptical orbits close to the Sun Or Captured by Saturn as outer satellites
Jupiter-family: Kuiper belt 20 years. Gravitational perturbations by Neptune Elliptical orbits close to the Sun Or Captured by Saturn as outer satellites
Comets and their periodsComets and their periods Oort Cloud Comets
Intermediate-periods: period 20 - 200 years Long-periods: period 1-3 million years Orbits steeply inclined to the plane of ecliptic Spend most of their time 10,000 to 100000 AU from
Sun About 1 long-period comet is discovered every month It is thought that many of these comets were icy
planetesimals that orbited the Sun and were near the Jovian planets when the solar system was formed. Gravity from the Jovian planets catapulted these objects into outer space.
Oort Cloud Comets Intermediate-periods: period 20 - 200 years Long-periods: period 1-3 million years Orbits steeply inclined to the plane of ecliptic Spend most of their time 10,000 to 100000 AU from
Sun About 1 long-period comet is discovered every month It is thought that many of these comets were icy
planetesimals that orbited the Sun and were near the Jovian planets when the solar system was formed. Gravity from the Jovian planets catapulted these objects into outer space.
Sun Grazing CometsSun Grazing Comets
These Comets come very close to the Sun and can also fall into the Sun.
These Comets come very close to the Sun and can also fall into the Sun.
Courtesy: SOHO, NASA
Twin Comets Eruptive performance
Hydrogen Envelope of CometHydrogen Envelope of Comet When the Comet approaches the Sun, it nucleus
begins to vaporizes creating a hydrogen gas envelope around it. This envelope is not visible to the naked eye.
The hydrogen in the envelope comes from water molecules breaking up when they absorb the ultraviolet photons from the Sun.
The hydrogen atoms also absorb ultraviolet photons and can only be detected by space based telescope (Earths atmosphere absorbs UV radiation) when they emit back ultraviolet radiation.
When the Comet approaches the Sun, it nucleus begins to vaporizes creating a hydrogen gas envelope around it. This envelope is not visible to the naked eye.
The hydrogen in the envelope comes from water molecules breaking up when they absorb the ultraviolet photons from the Sun.
The hydrogen atoms also absorb ultraviolet photons and can only be detected by space based telescope (Earths atmosphere absorbs UV radiation) when they emit back ultraviolet radiation.
Comets TailsComets Tails Ludwig Biermann propose the idea of solar
wind to explain comet tails. Mariner 2 spacecraft captured the one such event in 1962.
Ludwig Biermann propose the idea of solar wind to explain comet tails. Mariner 2 spacecraft captured the one such event in 1962.
Comets TailsComets Tails The solar wind produces three Comet tails that
point away from the motion of the Comet. The blue ion tails is ionized atoms of CN and C2. The dust tail is produced when the photons from the
Sun strike the dust particles and produce radiation pressure on them. This causes the dust particles to drift away from the come. The effect of solar wind on dust particles is less compared to
that on ions, this gives the dust tails a curved shape. The third tail is made up of Sodium and is usually
invisible to the unaided eyes.
The solar wind produces three Comet tails that point away from the motion of the Comet. The blue ion tails is ionized atoms of CN and C2. The dust tail is produced when the photons from the
Sun strike the dust particles and produce radiation pressure on them. This causes the dust particles to drift away from the come. The effect of solar wind on dust particles is less compared to
that on ions, this gives the dust tails a curved shape. The third tail is made up of Sodium and is usually
invisible to the unaided eyes.
Basic Physics of CometsBasic Physics of Comets
Comets obey Kepler laws of planetary motion, Newton law’s of motion and Newton’s law of gravity.
Nucleus Density = Mass /Volume ≈ 1000 kg/m3
From Kepler’s 3rd Law the aphelion distance can be determined (Period in years)2 = (aphelion distance in AU)3
Comets obey Kepler laws of planetary motion, Newton law’s of motion and Newton’s law of gravity.
Nucleus Density = Mass /Volume ≈ 1000 kg/m3
From Kepler’s 3rd Law the aphelion distance can be determined (Period in years)2 = (aphelion distance in AU)3
Basic Physics of CometsBasic Physics of Comets
The tidal force on the Comet can be estimated from: Force = (Solar Mass)(Comet Radius)/
(distance)3
The brightness of a Comet can be determined from: Brightness œ (distance from Sun) - n (distance from
earth) - 2
Near the sun n ≈ 4
The tidal force on the Comet can be estimated from: Force = (Solar Mass)(Comet Radius)/
(distance)3
The brightness of a Comet can be determined from: Brightness œ (distance from Sun) - n (distance from
earth) - 2
Near the sun n ≈ 4
Basic Physics of CometsBasic Physics of Comets
The linear size of any object in the sky can be determined by the small angle formula:
The linear size of any object in the sky can be determined by the small angle formula:
D d206,265
360 60 60
2206,265
is in arc seconds
Linear Size D
Distance d
Angular Size
Eye
Comets and their SpectraComets and their Spectra
Spectroscopy is a technique in which light is broken into its component colors. Each chemical element show their fingerprint in the spectrum of the object.
We can thus find the composition of Comets by identifying the fingerprints.
Most of the information on Comets come from Infrared radiation, because Comets are cold objects they radiate strongly at Infrared radiation.
Spectroscopy is a technique in which light is broken into its component colors. Each chemical element show their fingerprint in the spectrum of the object.
We can thus find the composition of Comets by identifying the fingerprints.
Most of the information on Comets come from Infrared radiation, because Comets are cold objects they radiate strongly at Infrared radiation.
Observed CompositionObserved Composition
Coma H, C, C2, C3, CH, CN, HCN, CH3, NH, NH2, O, OH,
H2O, Na, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu plus dust particles with silicates
Tail CH+, CO+, CO2
+, N2+, OH+, H2O+, Ca+, plus dust
particles with silicates
Coma H, C, C2, C3, CH, CN, HCN, CH3, NH, NH2, O, OH,
H2O, Na, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu plus dust particles with silicates
Tail CH+, CO+, CO2
+, N2+, OH+, H2O+, Ca+, plus dust
particles with silicates
Comet CollisionsComet Collisions
Comet collision with Earth can bring devastation to life on Earth.
Jupiter in our solar system is the largest planet and thus exerts greater gravitational pull on incoming Comets.
Study of Shoemaker-Levey collision with Jupiter gave us important facts about Comet collisions.
Comet collision with Earth can bring devastation to life on Earth.
Jupiter in our solar system is the largest planet and thus exerts greater gravitational pull on incoming Comets.
Study of Shoemaker-Levey collision with Jupiter gave us important facts about Comet collisions.
Comet CollisionsComet Collisions
Courtesy: NASA/JPL
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